1. Field of the Invention
The invention is related to a method for controlling a grid of plants, where each plant includes a distributed control system with operation and monitoring functionality, comprising the step of interconnecting the distributed control systems via a network.
2. Description of the Related Art
The current state of distributed control systems (DCS) for any type of plants like refineries or in particular power generation plants is to have one DCS with operation and monitoring (O&M) functionality per plant. The entire range of O&M functionality includes functions such as configuration/engineering of units, generating dynamic plant displays, archiving of process data, generating reports, providing alarming and diagnostic functionality. The DCS allows operating and monitoring the whole plant and its local generation units by several human machine interface (HMI) clients on the same site.
This kind of plant-specific DCS does not cover the situation of having a grid of multiple (geographically) distributed plants/units that need to be operated and monitored. The units may be small (e.g., wind turbines) or larger and of different kinds. In the following context the terms “unit” or “plant” are related to a power generating entity. One approach for a solution of control of such distributed units is called SCADA (supervisory control and data acquisition). In the SCADA approach, all (geographically distributed) units are connected via a network to a central control room, and supervision and control of these units are centralized in the control room. Each plant site or even each unit of a plant site contains the engineering and process values of its plant/unit's automation and information systems. This process image (i.e., the collection of dynamic process values) is available for the local subordinate SCADA system and on the remote superordinate systems. The superordinate SCADA system contains its own engineering and process values and all process images of its subordinate SCADA systems. Although the process image of a subordinated system located on the superordinate SCADA system is equal to the process image of the subordinate SCADA system apart from being connected to the subordinate system, the process images must be engineered again for the superordinate unit (inclusive plant displays, or alarm lists).
As current SCADA systems operate with a single process image, it results in one big process image hosting all data from all process images of its own and all subordinate systems. From this, it follows the SCADA system on the superordinate unit does not scale with the amount of subordinate units resulting in exceeding the limits of resources like memory or CPU load. Furthermore, required changes to the engineering of a subordinate system have to be retightened on the superordinate system. This includes all changes made to the process image and the plant displays.